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Abstract

The two domain HIV binding protein sCD4-183 undergoes guanidine hydrochloride (Gdn-HCl) induced unfolding via a two-step mechanism during which both domains unfold. The events of unfolding have been found to occur at 0.6(±0.2) M and 2.0 (± 0.1) M with changes in free energy at 23"C of 1.9(± 0.4) and 2.8(±
0.2) kcal/mol respectively by the linear-extrapolation method. Spectroscopic
methods of absorption, fluorescence, and circular dichroism were used to probe
aromatic amino acids in order to determine unfolding events. In addition, the
fluorescent probes 1,8-anilinonaphthalene sulfonate (ANS) and 6-propionyl 2dimethyl-
amino-naphthalene (PRODAN) were used to further characterize protein unfolding.